The patch titled
Subject: x86/uaccess: avoid check_object_size() in copy_from_user_nmi()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: x86/uaccess: avoid check_object_size() in copy_from_user_nmi()
Date: Mon, 19 Sep 2022 13:16:48 -0700
The check_object_size() helper under CONFIG_HARDENED_USERCOPY is designed
to skip any checks where the length is known at compile time as a
reasonable heuristic to avoid "likely known-good" cases. However, it can
only do this when the copy_*_user() helpers are, themselves, inline too.
Using find_vmap_area() requires taking a spinlock. The
check_object_size() helper can call find_vmap_area() when the destination
is in vmap memory. If show_regs() is called in interrupt context, it will
attempt a call to copy_from_user_nmi(), which may call check_object_size()
and then find_vmap_area(). If something in normal context happens to be
in the middle of calling find_vmap_area() (with the spinlock held), the
interrupt handler will hang forever.
The copy_from_user_nmi() call is actually being called with a fixed-size
length, so check_object_size() should never have been called in the first
place. Given the narrow constraints, just replace the
__copy_from_user_inatomic() call with an open-coded version that calls
only into the sanitizers and not check_object_size(), followed by a call
to raw_copy_from_user().
Link: https://lkml.kernel.org/r/20220919201648.2250764-1-keescook@xxxxxxxxxxxx
Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@xxxxxxxxxxxxxx
Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reported-by: <dev@xxxxxxxxxxx>
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/arch/x86/lib/usercopy.c~x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi
+++ a/arch/x86/lib/usercopy.c
@@ -44,7 +44,8 @@ copy_from_user_nmi(void *to, const void
* called from other contexts.
*/
pagefault_disable();
- ret = __copy_from_user_inatomic(to, from, n);
+ instrument_copy_from_user(to, from, n);
+ ret = raw_copy_from_user(to, from, n);
pagefault_enable();
return ret;
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch
